This invention relates to a pump apparatus used, for example, in a hydraulic brake system of a vehicle, and more particularly to a technique of reducing noises and vibrations produced by the operation of a pump.
Generally, a conventional pump apparatus of this type comprises a plunger whose one end portion is fitted in a cylinder bore, formed in a body, to form, together with this cylinder bore, a pressure chamber, an eccentric cam provided adjacent to the other end of the plunger so as to move the plunger toward the pressure chamber, a drive shaft which supports the eccentric cam and extends in a direction intersecting the axis of the plunger, and an output shaft of a motor for imparting a rotational force to the drive shaft. Connection between the drive shaft and the output shaft is made by the fitting of a convex portion in a concave portion, the convex portion being formed on one end of one of the drive shaft and the output shaft whereas the concave portion is formed in one end of the other. Both a pump apparatus with one plunger and a dual-type pump apparatus with two plungers have such a construction. The former is disclosed in Japanese Utility Model Publication No. 24375/80 (corresponding to U.S. Pat. No. 3,612,728), and the latter is disclosed in Japanese Laid-Open (Kokai) Utility Model Application No. 19079/89.
In such a pump apparatus, to facilitate the connection between the drive shaft and the output shaft, or to facilitate the attachment of the motor to the pump, it is desirable that the convex portion and the concave portion, provided respectively at the ends of the drive shaft and the output shaft, should be fittingly engaged with each other with clearances therebetween. Such a clearance provided at each side of the convex portion is, for example, about 0.1 to 0.15 mm.
However, when such clearances are provided, it has been found that the convex portion and the concave portion are not always held in contact with each other in the direction of the periphery of the two shafts, which causes noises and vibrations. More specifically, when the rotational force is varied due to the activation of the motor or the pumping action, the position of the convex and concave portions relative to each other in the peripheral direction is changed, so that the convex and concave portions are brought into contact or out of contact with each other. As a result, noises and vibrations are produced when the convex and concave portions impinge upon each other.
Such noises and vibrations are undesirable from the viewpoint of the durability of the pump apparatus, and besides when the pump apparatus is mounted on a vehicle, such noises and vibrations cause the driver to feel uncomfortable when the sound generated from the vehicle is at a low level, as during the idling of the engine.